By far the best-known part of the National Coal Board's film work is the long-running Mining Review series. Yet it only accounts for about a third of the NCB's total screen output. Most of the remaining 700 or so productions were one-off shorts that could broadly be described as documentaries. Certainly, they match the rather fuzzy template for 'documentary' as evolved during the 1930s and 1940s (allowing for much use of reconstructed, even purely fictional, content, and its use for highly practical industrial purposes). The professional origins of the NCB's senior filmmakers having been in the British 'documentary movement' this is unsurprising. In fact, there is good evidence that they viewed Mining Review itself more as an extension of documentary than as an incursion into newsreel. Many of its less topical stories are essentially mini-documentaries, often made by the same personnel as the single productions - sometimes repurposed as films in their own right, or themselves cut down from longer films. For example, Wagon Handling at Dalkeith (1953), was a technical documentary which later provided the footage for 'Wagon Wheels', the opening item of Mining Review 7th Year No 7.

DATA, the cooperative responsible for producing every edition of Mining Review between 1947 and 1962, also took on one-off commissions from the Coal Board (as it did from other sponsors). An important one was Plan for Coal (1952), a stentorian public address heavily reminiscent of the most pressing of Churchillian wartime films in hitting home the importance of industry reorganisation plans. But the NCB occasionally received films from other significant documentary units like Basic Films, World Wide Pictures and even, on one occasion (1952's Under the Surface), Gaumont-British Instructional.

After the formation of the NCB's own film unit, its first films coming in 1953, most documentaries were produced in-house while DATA continued to supply Mining Review until 1962. Of the few exceptions, by far the most important is Derrick Knight's A Time to Heal (1963), made by Knight's own company, and jointly sponsored by the NCB with the Coal Industry Social Welfare Organisation, which both the Board and the union were involved in running. This poignant film about injury rehabilitation pioneered the incorporation of a modern hand-held and synch-sound style, reminiscent of American Direct Cinema, into British industrial filmmaking.

Some NCB films, like Basic's ambitious Nine Centuries of Coal (1958), were treatments of the history or science of coal-mining intended for classroom use. Others were made for recruitment purposes (one example, among many, being the NCB Film Unit's We Choose To Be Miners, 1961). However, the majority of the output consisted of highly esoteric documentaries intended mainly or solely for staff, and for use in training. The most frequent common theme reflected by the earlier films is the speed, scale and technical intricacy of the revolution in mining techniques brought about by the NCB's modernisation programme, and in particular by the almost complete shift to mechanised coal getting. Occasionally, 'state-of-the-industry' statements were addressed to the general public as well as to miners themselves, as in the punchy New Power In Their Hands (1959), which draws on the growing library of footage yielded by the specialist films. Of the few longer films aimed mainly at non-mining audiences, most were general interest shorts destined for the non-theatrical circuit (in the 1970s a number of these were even made, as full-length issues of Review or spin-off projects, for outside sponsors: these were entirely devoid of mining industry content).

The adventurous exceptions, mostly made between the mid-1960s and mid-1970s, show the NCB Film Unit (particularly its younger members) stretching out in an effort to connect this most conservative of industries with the zeitgeist of a rapidly changing society. Sometimes, they emulate British Transport Films' comparable but undoubtedly more prestigious output - King George V (1970) even takes a historical locomotive as its subject - but some are more unusual.

Australian director Richard Mason's Portrait of a Miner (1966) is a half-hour film applying techniques from youthful contemporary cinema to the age-old subject of a miner's working day, complete with allusions to sexuality, psychology and generational differences that would have been unthinkable in the output of a few years earlier. It is a slightly dated but strikingly ambitious attempt to update the drama-documentary form. Master Singers - Two Choirs and A Valley (1965) was a beautifully evocative co-production with the BBC helmed by Robert Vas (soon to be one of the Corporation's star documentary directors, Vas was for some years a regular NCB editor). The Big Meeting (1963) is a warm, well-photographed tribute to miners' galas, Peter Pickering's Two Worlds (1965) a peculiar essay on relationships between coal technologies, education and social change.

Unlike these films, most NCB documentaries continued to be screened mainly to miners, their managers and other Board employees - still meaning, of course, a potential audience of tens of thousands. While many of the films concerned with machinery and technical training are straightforward instructions, others contain graphic, darkly humorous (and sometimes cheerfully sexist) content appealing to their target audience. Euan Pearson's Safeguards With Machinery (1967) for example, includes a vivid sequence in which poor equipment handling leads to a miner's foot being sliced off!

Some of the most interesting films betray a darker perspective on industrial relations and economic pressures than the normally relentless cheer of Mining Review would ever have permitted. As early as 1949, a film like Nines Was Standing (the sole NCB film made by the important independent documentary company, Greenpark Productions) has to acknowledge the existence of miners' scepticism about pit consultative committees as part of its argument in favour of them. But it is films made after 1957, and that year's sudden crisis in the industry, brought on by plummeting oil prices and clean air legislation, that most fascinatingly engage with the industry's new predicaments. This was reflected not only in the first sales films being made, to help coal beat off the competition, but in internal films focused on staff motivation and employee relations.

Experiment (1958), directed by NCB Films Officer Donald Alexander (and shelved before getting much of a release), indicates that union intervention had ensured that 'method study' would go ahead but only on a strictly limited basis. Pickering's The Team on 204's (1964) and The Longhirst Story (1967), are carefully low-key but optimistic case studies of mechanisation and productivity increases. But their flip-side is the same director's Nobody's Face (1966) and Who's Driving (1971): cynical comedies of error set in fictional collieries in which circumstance conspires with incompetence to create massive inefficiency. However tentatively, they confront complacency in both managers and workers, already hit by huge colliery and job losses, suggesting the paradox upon which the NCB was founded: a state corporation, publicly owned yet needing to survive in a mixed economy, and - we now know - with a relatively short future ahead of it.

As a body of work, the National Coal Board's documentary legacy has much going for it. Its scale is mightily impressive. Unquestionably, it is riddled with fascination for students of post-war ideology - though as often for what's left out as for what's included. It is frequently well made and entertaining. Nonetheless, to base an argument for the collection's value on its artistic contribution to the documentary form would be largely beside the point of the filmmakers' (certainly of the NCB's own) main intentions. In the long run their greatest gift to the future is probably their technical coverage of the underground professional world daily inhabited by so many British men for so many years. No other filmmakers had such prolonged exposure to it, nor recorded it in as much detail.